1. Field of the Invention
The present invention relates to an image processing device enabling observation under a plurality kinds of observation light.
2. Description of the Related Art
Electronic endoscopes are designed to be inserted into body cavities and the like and widely used to observe the alimentary tract including the esophagus, stomach, small intestine, and large intestine or the trachea such as lungs. The electronic endoscope is also adapted to various kinds of treatment or cure that are performed using a treatment instrument passed through a treatment instrument channel.
For example, in a field-sequential endoscope system, light emanating from a light source unit is passed through an optical filter in order to sequentially irradiate red, green, blue light and the like to an object. A monochrome image pickup device receives the lights reflected from the object. A processor (signal processing unit) performs signal processing on an output signal of the image pickup device. Eventually, a color image is displayed on a display device.
The signal processing to be performed in the processor includes color enhancement that is intended to help discover a lesion. In the color enhancement, a color is enhanced using an amount of hemoglobin contained in the mucosa of a living body as a criterion. This helps distinguish a normal mucosa from an abnormal mucosa on the basis of a difference in color.
Moreover, when an endoscope is used for diagnosis, normal observation is performed in order to display a color image, which depicts an object in the same manner as the object is seen with the naked eyes, on a monitor. In addition, self-fluorescent observation that utilizes light resulting from self-fluorescence of a living-body tissue is prevailing. In the self-fluorescent observation, the spectral characteristic of self-fluorescent light deriving from fluorescence of a living-body tissue caused with excitation light whose wavelengths range from the infrared region of the electromagnetic spectrum to the blue region thereof varies depending on whether the living-body tissue is a normal mucosa or a tumor.
Diagnosis is performed by utilizing the fact that the spectral characteristic of self-fluorescent light varies depending on whether a living-body tissue is a normal mucosa or a tumor.
An image represented by self-fluorescent light and an image represented by light reflected from a living-body tissue are assigned different colors and displayed on a monitor. Consequently, a lesion can be clearly identified based on a difference in color from a normal region.
Moreover, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-95635, narrow-band light observation (or narrow-band imaging (NBI)) is adopted as observation under light whose wavelengths fall within a narrower band than the wavelengths of normal observation light. In the narrow-band light observation, the vessels in the mucosal membrane can be observed with a higher contrast.
Since the narrow-band light observation is observation under narrow-band light, an image whose color tone is different from the color tone of a normal endoscopic image is displayed. A color conversion circuit is therefore incorporated in a processor in order to adjust colors. After the color tone is converted into a color tone more helpful in distinguishing a lesion, the image is displayed on the monitor.
Moreover, infrared observation that is observation under near infrared light is popular. During infrared observation, a chemical agent called indocyanine green (ICG) to which near infrared light is absorbed is injected into the vessel. Consequently, the vascular kinetics in a submucous deep region that is not visualized by normal observation can be observed. Even during the infrared observation, if color enhancement is performed using an amount of ICG contained in the mucosa as a criterion, the vessels can be observed with a higher contrast.
The facilities for performing the foregoing normal observation, fluorescent observation, narrow-band light observation, and infrared observation may be implemented in one system by employing a lighting unit capable of switching illumination lights.
In order to reduce the scale of the circuitry of an endoscope system, as disclosed in Japanese Unexamined Patent Application Publication No. 5-277065 (Japanese Patent No. 3382973), a programmable logic element is included for each of charge-coupled devices (CCDs) incorporated in endoscopes to be connected. Thus, the same circuit is used in common in different facilities.